1. Technical Field
The present invention relates to a control device of an internal combustion engine for controlling the internal combustion engine. It should be noted that hereinafter, the internal combustion engine is also simply called as the “engine”.
2. Related Art
Conventionally, there is a widely known control device of an internal combustion engine for performing feedback control on an air-fuel ratio of fuel-mixing air (hereinafter, also simply called as the “air-fuel ratio of the engine”) supplied to the engine based on output values of an upstream air-fuel ratio sensor and a downstream air-fuel ratio sensor respectively arranged in an exhaust passage on the upstream side and the downstream side of a ternary catalyst (hereinafter, also simply called as the “catalyst”). In such a control device, the upstream air-fuel ratio sensor and the downstream air-fuel ratio sensor detect air-fuel ratios of an exhaust gas discharged from cylinders of the internal combustion engine to pass through the exhaust passage (hereinafter, called as the “mixing exhaust gas”). An air-fuel ratio feedback amount is calculated using the air-fuel ratios detected by these sensors. By adjusting an amount of fuel to be respectively jetted to the plurality of cylinders based on this air-fuel ratio feedback amount, the feedback control is performed in a manner that the air-fuel ratio of the engine matches a target air-fuel ratio.
Regarding such air-fuel ratio control, for example, the following Patent Document 1 discloses an exhaust emission purification device that sets a target air-fuel ratio (hereinafter, also called as the upstream target air-fuel ratio) of an air-fuel ratio of an engine (that is, an air-fuel ratio of a mixing exhaust gas flowing into a catalyst) in accordance with an atmosphere in an interior of the catalyst (that is, a reduction atmosphere or an oxidation atmosphere). This conventional exhaust emission purification device is provided with a catalyst atmosphere detection means that detects whether an atmosphere of a catalytic converter is the reduction atmosphere or the oxidation atmosphere by a second exhaust gas detection means (downstream air-fuel ratio sensor) provided on the downstream side of the catalytic converter, and also provided with a catalyst atmosphere adjustment means for, when an exhaust gas purification state by the catalytic converter is degraded, in accordance with a detection result of the catalyst atmosphere detection means, adjusting the atmosphere of the catalytic converter into an atmosphere different from the detection result. In this case, specifically, the internal combustion engine is provided with an air-fuel ratio forcible alteration means capable of forcibly altering the air-fuel ratio between an air-fuel ratio on the rich side and an air-fuel ratio on the lean side at predetermined cycles and amplitudes. The catalyst atmosphere adjustment means adjusts an altering degree between the air-fuel ratio on the lean side and the air-fuel ratio on the rich side of the air-fuel ratio forcible alteration means in accordance with the detection result of the catalyst atmosphere detection means.
In recent years, alcohol such as ethanol is sometimes included in gasoline supplied to the engine as the fuel. For example, mainly known ethanol-containing gasoline fuel used for a so-called FFV (Flexible Fuel Vehicle) includes “E3” with 3% of ethanol concentration, “E85” with 85% of the same concentration, and “E100” of 100%-ethanol fuel. The ethanol concentration largely varies. It should be noted that in the case where alcohol is included in gasoline, such mixing fuel of gasoline and alcohol is hereinafter called as the “alcohol-mixing fuel” or simply called as the “fuel”.
When such alcohol-mixing fuel is supplied to the engine, hydrogen concentration in the mixing exhaust gas is increased in comparison to the case where the fuel only made of gasoline is supplied to the engine. When the hydrogen concentration in the mixing exhaust gas is increased in such a way, hydrogen concentration in the interior of the catalyst arranged in the exhaust passage is also increased due to the mixing exhaust gas passing through. Since hydrogen acts as a so-called strongly reducing agent, by increasing the hydrogen concentration in the interior of the catalyst, the atmosphere in the interior of the catalyst becomes the reduction atmosphere.
Therefore, in the case where the feedback control is performed by altering the upstream target air-fuel ratio based on the detection result of the atmosphere of the catalytic converter by the second exhaust gas detection means (downstream air-fuel ratio sensor) as in the above conventional exhaust emission purification device, upon supplying the alcohol mixing fuel to the engine, there is a possibility that the second exhaust gas detection means (downstream air-fuel ratio sensor) falsely determines that the atmosphere in the interior of the catalytic converter is the oxidation atmosphere even when the atmosphere is the reduction atmosphere. As a result, there is sometimes a case where proper setting in accordance with the atmosphere in the interior of the catalyst cannot be performed. Regarding this point, the following Patent Document 2 shows that in an internal combustion engine to which alcohol mixing fuel can be supplied, a discrepancy of a detected value of a downstream air-fuel ratio sensor (oxygen concentration sensor) arranged on the downstream side of a catalyst is corrected in accordance with concentration of alcohol included in the alcohol mixing fuel (hereinafter, called as the “alcohol concentration”).